Molding of various plastic materials is a common method used to create parts for various applications. One specific method of producing parts in this manner is through the use of a sheet molding compound (SMC). Several examples of thermoset composite molding are Sheet Molding Compound (SMC), Long Fiber Injection (LFI), Structural Reaction Injection Molding (SRIM), Reinforced Reaction Injection Molding (RRIM), or Vacuum Assisted Resin Transfer Molding (VARTM).
The method of making a part using LFI involves the use of fiberglass cut into long strands, or fibers, mixed with a resin to provide additional strength to a molded part. SRIM molding is similar to typical injection molding, except that thermosetting polymers are used, and the two parts of the polymer are mixed together and injected into a mold under high pressure, and are then allowed to cure. A reinforcing agent is used, such as glass fillers, in the mixture for improved strength. RRIM is another type of SRIM, in which a fiber mesh is used as the reinforcing agent; the fiber mesh is placed in the mold and the polymer mixture is then injection molded over it. VARTM is a process in which resin is inserted into a mold which contains layers of fibers or a preform; flow of resin is assisted by a vacuum in the mold.
Typical SMC sheet processing allows or results in several issues, including, a dry edge without needed characteristics or properties, a glass rich or resin rich mixture (e.g., not a homogeneous mixture of glass and resin in the SMC sheet), styrene release leading to unusable material, and wasted material on the edges of the SMC sheet.
There has been an increasing desire to create parts molded of one or more layers of SMC. Having layers of carrier film sealed on the edge of the sheet will reduce waste while more effectively producing SMC having suitable properties.
To try to overcome the issues described above, heat sealing edges of the carrier films has been employed. However, heat sealing has several disadvantages, for example, heat sensitivity, periodic replacement of heater belts, inconsistent burning of the film leading to over-seals, and the solid seal does not allow air to escape which traps air bubbles in the film.
Accordingly, there exists a need for a method of producing SMC carrier films by ultrasonic sealing the edges of the sheet which ensures moldable SMC flow to the edges to reduce waste, while allowing SMC material flow and homogeneous mixing.